1 . Field of the Invention
The present invention generally relates to a downhole tool for use in a wellbore. More particularly, the invention relates to isolating an area of interest within a wellbore. More particularly still, the invention relates to anchoring an expandable tubular within the wellbore prior to isolating the wellbore.
2 . Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is typically lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore.
Generally, it is desirable to provide a flow path for hydrocarbons from the surrounding formation into the newly formed wellbore. Typically, perforations are formed in the casing or in the open hole portion of the wellbore at the anticipated depth of hydrocarbons. The perforations are strategically formed adjacent the hydrocarbon zones to limit the production of water from water rich zones that may be close to the hydrocarbon rich zones. However, a problem arises in a cased wellbore when the cement does not adhere to the wellbore properly to provide an effective fluid seal. The ineffective seal allows water to travel along the cement and wellbore interface to the hydrocarbon rich zone. As a result, water or gas may be produced along with the hydrocarbons.
One attempt to solve this problem is to employ a downhole packer, commonly an inflatable packer, to isolate specific portions of the wellbore. The downhole packer may be installed as an open-hole completion to isolate a portion of the wellbore and eliminate the need of cementing the annular area between the casing and the wellbore of the isolated portion. Typically, the downhole packer may be formed as an integral member of the existing casing and installed adjacent the desired production zone.
More recently, expandable tubular technology has been applied to downhole packers. Generally, expandable technology enables a smaller diameter tubular to pass through a larger diameter tubular, and thereafter expanded to a larger diameter. In this respect, expandable technology permits the formation of a tubular string having a substantially constant inner diameter. Accordingly, an expandable packer may be lowered into the wellbore and expanded into contact with the wellbore. By adopting the expandable technology, the expandable packer allows a larger diameter production tubing to be used because the conventional packer mandrel and valving system are no longer necessary.
When an expandable tubular is run into a wellbore, it must be anchored within the wellbore at the desired depth to prevent rotation of the expandable tubular during the expansion process. Anchoring the expandable tubular within the wellbore allows expansion of the length of the expandable tubular into the wellbore by an expander tool. The anchor must provide adequate frictional engagement between the expandable tubular and the inner diameter of the wellbore to stabilize the expandable tubular against rotational and longitudinal axial movement within the wellbore during the expansion process.
The expandable tubular used to isolate the area of interest is often run into the wellbore after previous strings of casing are already set within the wellbore. The expandable tubular for isolating the area of interest must be run through the inner diameter of the previous strings of casing to reach the portion of the open hole wellbore slated for isolation, which is located below the previously set strings of casing. Accordingly, the outer diameter of the anchor and the expandable tubular must be smaller than all previous casing strings lining the wellbore in order to run through the liner to the depth at which the open hole wellbore exists.
Additionally, once the expandable tubular reaches the open hole portion of the wellbore below the casing liner, the inner diameter of the open hole portion of the wellbore is often larger than the inner diameter of the casing liner. To hold the expandable tubular in place within the open hole portion of the wellbore before initiating the expansion process, the anchor must have a large enough outer diameter to sufficiently fix the expandable tubular at a position within the open hole wellbore before the expansion process begins.
There is a need for an anchor to support an expandable tubular used to isolate an area of interest within a wellbore prior to initiating and during the expansion of the expandable tubular. There is a need for an anchor which is small enough to run through the previous casing liner in the wellbore, capable of expanding to a large enough diameter to frictionally engage the inner diameter of the open hole wellbore below the casing liner, and capable of holding the expandable tubular in position axially and rotationally during the expansion of the length of the expandable tubular.